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SACUS: WTZ Südliches Afrika - SACUS-SPACES: Southwest African Coastal Upwelling System and Benguela Ninos

Coastal countries of southwest Africa strongly depend upon their ocean: societal development, fisheries, and tourism face important changes associated with climate variability and global change. Global climate change will particularly impact eastern boundary upwelling regions by a combination of different stressors: increasing temperatures, acidification and deoxygenation (Gruber et al. 2011). The main focus of the proposed study is on the coastal upwelling off southern Africa (Fig. 1), its variability forced locally by the wind field and remotely by wave propagation and water mass advection from the equatorial region, its response to climate change, and its impact on rainfall of the region. It will address physical mechanisms of regional climate variability with profound impact on ocean biogeochemistry, hypoxia and marine ecosystems. We will use dedicated observing systems, experiments at sea as well as various modeling approaches in order to study intraseasonal to long term changes of the southwest African coastal upwelling system (SACUS) and the overlying atmosphere to finally improve climate prediction for southern Africa. The project aims at building and expanding local capacities required for the monitoring and prediction of the variability of the upwelling system and of the climate of surrounding land areas by cooperative research, joint summer/winter schools and scientist/technician exchange, by teaching of PhD and Master Students from southern African countries at German Universities, by research cruises open for southern African participants and by providing data and model output for analysis at southern African universities and institutes.

The SACUS subproject II investigates the interaction of the Angola Gyre with the Benguela upwelling system. Both the systems are linked by the eastern boundary currents which act as a pole-ward conveyer of South Atlantic Central Water (SACW). The export of this suboxic and nutrient rich water into the Angola current and the Benguela system is a key process for the Benguela ecosystem, since the SACW is one of the source water masses of the Benguela upwelling. Little is known about the variability of the eastern boundary currents in relation to remote forcing in the equatorial area and its modification in response to the local winds. These questions will be addressed by both, fields measurements with moorings along the Angolan and Namibian coastline combined with remote sensing data, and by analytical and numerical model studies. The time dependent pole-ward transport of SACW with the Angola current through the Angola Benguela Frontal Zone (ABFZ) will be measured at several positions and the correlations to remote forces and local winds will be analysed. Numerical experiments with passive tracers will be carried out to study the pathways and transformation of water masses in a numerical ocean circulation model.

Publikationen

  • Junker, T., V. Mohrholz, L. Siegfried and A. van der Plas (2017). Seasonal to interannual variability of water mass characteristics and currents on the Namibian shelf. J. Mar. Syst. 165: 36-46, doi: 10.1016/j.jmarsys.2016.09.003